Antimicrobial compositions



l ltwlslili Claims. (Cl. 16731) This invention relates to novel compositions and to methods for controlling microbial contamination in ecow' nomically important organic suspensions and emulsions Many aqueo organic emulsions and suspensions, which can be classed generically as aqueous organic colloids, are prone to attack by numerous microorganisms, including bacteria, yeasts and fungi. Because of the industrial importance of a number of these organic colloids, it is desirable to protect them from microbial attack, or alternatively, to eliminate bacterial or fungal growth if already initiated. The contaminating microorganisms are chiefly yeasts or non-pathogenic gram negative rods, although some pathogenic organisms including bacteria and fungi can also be present, thus constituting a definite industrial hygienic hazard. To date, no preservative or combination of preservatives has been available which is broadly utilizable in preventing microbial contamination in industrially important organic emulsions and suspensions.

Illustrative industrially important colloids which it is desirable to protect from microbial contamination or, which having already been contaminated, desirably should have their microbial population substantially decreased or eliminated, are emulsions such as polystyrenebutadiene emulsions fgnpaintiormulation, water oil emulsions such as the so-called soluble oil emulsioris eriipldyed for machining purposes, butter fat assay samples, latex emulsions, urethane foams, and suspensions and pastes such as starch paste, "W pulp, ca -base finger paints, and the like.

By preventing or decreasing microbial contamination in organic emulsions and suspensions of a character such as those mentioned above, both the shelf life and the useful life of the colloids can be increased. In the case of relatively rapidly processed materials, for example, wood pulp, the prevention of the growth of slime bacteria in the beaters and on the screens increases the time intervals between cleanings of the beaters and screens and thus reduces operating expense.

This invention provides novel compositions which, when incorporated in organic colloids of the above-described character, efiectively inhibit microbial growth and provide the advantages set forth above. The novel compositions comprise in combination ethylmercurithiosalicylic acid and o-phenylphenol, or their water-soluble, cationic salts. Suitable cationic salts include metal salts such as the sodium and potassium salts, and metalloid salts such as the ammonium and amine salts.

The relative proportions of the ethylmercurithiosalicylic acid and o-phenylphenol employed in the compositions of this invention can be varied over a wide range. It appears, however, that the broadest spectrum of antimicrobial effectiveness is attained when the o-phenylphenol is present in the combination in somewhat greater amount than the ethylmercurithiosalicylic acid. Hence, the preferred compositions comprise illustratively from about 4 to about 100 parts by weight of o-phenylphenol to each part by weight of ethylmercurithiosalicylic acid.

at'ented May 30, 1961 Maximum antimicrobial efiectiveness is generally attained when the compositions contain from about 10 to about 50 parts by weight of o-phenylphenol to each part by weight of ethylmercurithiosalicylic acid. The above ratios of ingredients are also employed when the ingredients are used in the form of their salts.

The novel compositions of this invention are readily prepared simply by adding in the desired amounts, the ethylmercurithiosalicylic acid or salt thereof and the o-phenylphenol or salt thereof, to the particular organic colloid which is to be protected from microbial attack. The antimicrobial agents can be incorporated individually in the colloid, but for general convenience and ease of use, the agents are usually combined in suitable proportions in a concentrate which is then added to the colloid in an amount sufficient to provide the desired antimicrobial action.

The concentrate can be in the form of a dry powder, or a solution, either aqueous or nonaqueous, or a suspension. The preferred concentrate is an aqueous solution of a suitably proportioned mixture of water-soluble salts of ethylmercurithiosalicylic acid and of o-phenylphenol, since such a concentrate can be easily added to and readily mixed with aqueous colloids such as suspensions and emulsions. Moreover, by providing a concentrate having relatively high concentrations of the antimicrobial agents, there will be no destruction of the stability of the emulsion or suspension upon the addition of v the concentrate causing it to break or to flocculate. Al-

ternatively, organic solvent solutions or suspensions of the antimicrobial agents or their salts can be employed in the provision of concentrates. Among the organic solvents useful for this purpose are xylene, alcohol, propylene glycol, polyethylene glycol, and the like.

If desired, the acid or salt forms of ethylmercurithiosalicylic acid and of o-phenylphenol can be incorporated directly into one or more of the ingredients of the emulsion or suspension prior to the preparation of the emulsion or suspension to provide protection against contamination from the moment the colloid is first pre pared. Thus, for example, sodium ethylmercurithiosalicylate and sodium o-phenylphenate can be incorporated into a powder consisting of starch casein, a pigment, and an emulsifier. Addition of water to the dry powder yields a finger paint composition which is preserved against microbial attack.

For effective microbial control, the ethylmercurithiosalicylic acid and the o-phenylphenol should be present in the organic colloid to be protected in the amount of about 10 to about 200 ppm. (parts per million by weight) of the former, and about to about 2000 p.p.m. of the latter. The concentrations to be employed are the same regardless of whether the antimicrobial agents are employed in their acid or salt forms.

The concentrations of the antimicrobial agents employed in the colloids depend upon a number of factors including the type of microbial contamination likely to be encountered, the relative resistance of the microorganisms, the degree of contamination, whether light or massive, and the like. In general it is desirable to employ concentrations approaching the upper values mentioned above in those colloids which are used in industrial areas where substantially continuous exposure to heavy contamination is a virtual certainty. On the other hand, much lower concentrations are required for the protection of colloids like paint formulations which are exvention comprising ethylmercurithiosalicylic acid and 0- 3 phenylphenol and their soluble salts are so highly effective in preserving organic colloids such as cutting oils, finger paints, latex emulsions and the like, since neither compound by itself will effectively prevent or control contamination of the colloids.

In certain of the industrially important organic colloids, such as soluble oil emulsions for machine tool shops which contain metal turnings and chips, there exists the probability of contamination of the emulsion by heavy metals, particularly copper. As is well known, ethylmercurithiosalicylic acid is destroyed over a period of time by the action of copper ions in the presence of oxygen, and it has been customary in the past to provide a stabilizer for the ethylmercurithiosalicylic acid if copper contamination was expected. The customarily employed ethylmercurithiosalicylic acid stabilizers, for example, ethylenediamine, ethanolamine, and ethylenediaminetetraacetic acid can be used in the compositions of this invention if only copper contamination is expected. However, if other heavy metals are also present, and in particular if iron is also present, other ethylmercurithiosalicylic acid stabilizers preferably are employed, including 8-hydroxyquinoline, bis salicylalethylenediamine, bis-salicylal-ophenylenediamine, and related compounds of similar stabilizing ability.

The quantity of ethylmercurithiosalicylic acid stabilizer which should be added to the organic emulsion or suspension which is to be preserved against bacterial and fungal attack, naturally depends upon the quantity of copper, iron, nickel, or other heavy metal contamination to be expected. However, for most industrial usages, the stabilizer should be present at the minimum in about the same concentration as the ethylmercurithiosalicylic acid, and at the maximum in about twice the concentration of ethylmercurithiosalicylic acid. Thus illustratively, a soluble oil emulsion for use with machine tools containing 50 p.p.m. of ethylmercurithiosalicylic acid and 1000 p.p.m. of o-phenylphenol as a preservative, would also contain from 50 to 100 p.p.m. of S-hydroxyquinoline or bis-salicylalethylenediamine as a stabilizer for the ethylmercurithiosalicylic acid. Likewise, a concentrate adapted for addition to a machine tool soluble oil emulsion, containing 2 percent ethylmercurithiosalicylic acid and 40 percent o-phenylphenol as their sodium salts, would contain from 2 to 4 percent of a stabilizer of the type set forth hereinabove.

This invention is further illustrated by the following specific examples:

Example 1 A water-soluble, antimicrobial dry powder composition is prepared by thoroughly mixing 15 pounds of finely divided sodium ethylmercurithiosalicylate and 205 pounds of finely divided sodium o-phenylphenate-tetrahydrate.

If desired, about 30 pounds of 8-hydroxyquinoline can be thoroughly mixed with the other ingredients to provide a stabilizing action for the sodium ethylmercurithiosalicylate at such time as the composition is incorporated for use in an aqueous emulsion or suspension.

The stabilized powder can be used as a preservative by adding it in the amount of about 0.13 pound per 1000 pounds of styrenebutadiene base paint employing casein as a modifier, to provide a final concentration in the paint of about 10 p.p.m. of sodium ethylmercurithiosalicylate, 20 p.p.m. of 8-hydroxyquinoline and about 100 p.p.m. of sodium o-phenylphenate.

Example 2 10 pounds of ethylmercurithiosalicylic acid and 200 pounds of o-phenylphenol are ground to a particle size averaging about 10a, are thoroughly blended, and are evenly distributed by etficient stirring in 100 gallons of an aqueous solution containing about percent by weight of methylcellulose of a viscosity of 4000 centipoises.

. One pound of the above suspension can be added to 400 pounds of soluble starch paste to provide a final concend tration in the paste of 25 p.p.m. of ethylmercurithiosalicylic acid and 500 p.p.m. of o-phenylphenol. The starch paste is thereby protected against microbial attack.

Example 3 10.15 pounds of ethylmercurithiosalicylic acid and 258 pounds of o-phenylphenol are dissolved in 39 gallons of xylene. To the solution is added as a stabilizer 20 pounds of bis-salicylal-o-phenylenediamine.

The above solution can be added in the amount of about 1 ounce per 5 gallons to inse'ed oil which is to be incorporated in various pa formulations, to provide paint compositions which remain substantially free from contamination by microorganisms.

Example 4 400 pounds of commercial sodium o-phenylphenate tetrahydrate containing about 2 percent excess sodium hydroxide and sodium carbonate are dissolved in 25 gallons of water. To the solution are added with stirring 20.3 pounds of ethylmercurithiosalicylic acid and 40 pounds of 8-hydroxyquinoline. The final volume is adjusted to 78 gallons by the addition of water. The solution contains sufiicient excess alkali so that the water-soluble sodium salts of the ethylmercurithiosalicylic acid and o phenylphenol are formed, and a clear solution results.

The aqueous concentrate can be added to a soluble oil emulsion employed for machining purposes in the amount of about 1 ounce of concentrate to each 5 gallons of emulsion to provide substantial freedom of the emulsion against attack by microorganisms.

A typical case showing the effectiveness of novel compositions of this invention in ridding a soluble oil emulsion of contamination by microorganisms is as follows:

A soluble oil emulsion was employed in a machine shop for a period of about 4 weeks and at the end of such time was rendered unfit for further use because of its heavy contamination by microorganisms. The emulsion was examined and was found to contain about 70,000,000 microorganisms per ml. of emulsion. Spectrographic analysis for its heavy metal content showed the presence of about 2 p.p.m. of copper, 1 p.p.m. of lead, 17 p.p.m. of iron, 18 p.p.m. of aluminum, 6 p.p.m. of molybdenum, and 13 p.p.m. of magnesium.

To the contaminated emulsion was added in the amount of about 1 ounce of solution for each 5 gallons of emulsion an aqueous solution containing 2 percent by weight of sodium ethylmercfirithiosalicylate, 40 percent by weight of sodium o-phenylphenate-tetrahydrate, and 4 percent by weight of bis-salicylal-o-phenylenediamine It was observed that after twenty-four hours the count of viable microorganisms had fallen to about zero. After four days of continued use in normal machining operations, a repeat count of viable microorganisms in the emulsion was made. The count of organisms was negligible, the microorganism being present in such minor numbers that there was no interference with the quality of the emulsion or with the use of the emulsion.

I claim:

1. A composition effective in inhibiting the growth of microorganisms in aqueous organic colloids, said composition comprising in admixture 1 part by weight of ethylmercurithiosalicylic acid and from about 4 to about 50 parts by weight of o-phenylphenol.

2. A composition according to claim 1 in which the ethylmercurithiosalicylic acid and o-phenylphenol are in the form of their water-soluble salts.

3. A composition effective in inhibiting the growth of microorganisms in aqueous organic colloids, said composition comprising in admixture about 1 part by weight of sodium ethylmercurithiosalicylate, and from about 4 to about 50' parts by weight of sodium o-phenylphenate.

4. An aqueous, organic colloid containing for antimicrobial action about 50 to about 200 p.p.m. of a member of the group consisting of ethylmercurithiosalicylic acid and its Water-soluble salts, and about 1,000 to about r 5 6 2,000 p.p.m. of a member of the group consisting of oto about 2,000 p.p.m. by Weight of a member of the group phenylphenol and its water-soluble salts. consisting of o-phenylphenol and its water-soluble salts.

5. The method of preventing microbial contamination of an aqueous organic colloid which comprises incorporat- References (Med me file of thls patent ing in said colloid about 50 to about 200 p.p.m. by weight 5 UNITED STATES PATENTS of a member of the group consisting of cthylmercurithio- 1,862,396 Khamsch J n 14 1932 salicylic acid and its water-soluble salts, and about 1,000 2 2 1 249 Roehm A 23, 1942 

5. THE METHOD OF PREVENTING MICROBIAL CONTAMINATION OF AN AQUEOUS ORGANIC COLLOID WHICH COMPRISES INCORPORATING IN SAID COLLOID ABOUT 50 TO ABOUT 20 P.PM. BY WEIGHT OF A MEMBER OF THE GROUP CONSISTING OF ETHYLMERCURITHIOSALICYLIC ACID AND ITS WATER-SOLUBLE SALTS, AND ABOUT 1,000 TO ABOUT 2,000 P.P.M. BY WEIGHT OF A MEMBER OF THE GROUP CONSISTING OF O-PHENYLPHENOL AND ITS WATER-SOLUBLE SALTS. 